Author: Song, Dongjin
Title: Optimizing the ultrasound echoes of electronic Bat Ears
Degree: M.Phil.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Ultrasonic transducers
Electroacoustic transducers
Department: Department of Rehabilitation Sciences
Pages: 92 leaves : ill. (some col.) ; 30 cm.
Language: English
Abstract: The electronic "Bat Ears" was designed to encode the spatial information of the physical environment with ultrasonic echoes and convert the spatial information into audible sound to guide people with visual disabilities. The electronic "Bat Ears" emits ultrasound pulses through a transducer (a transmitter located in the center) and receives the ultrasound echoes via two transducers (two receivers located on the left and right side). The ultrasound echoes detected by the two receivers are transformed to the audible frequency range. The binaural audio signals are delivered via two earphones. In the past few years, the electronic "Bat Ears" has been demonstrated to be effective for enhancing the mobility of people with early blindness. However, two problems have to be addressed to make the electronic "Bat Ears" calculate the accurate location of obstacles. Firstly, crosstalk between the transmitter and receivers affect the true ultrasound echo signals and thus, adversely affect the performance of the electronic "Bat Ears". Secondly, because the human auditory system considers two kinds of information, i.e., the interaural time differences (ITDs) and interaural intensity differences (IIDs), to localize the sound and the attenuation properties of ultrasound (high frequency) and sound (low frequency) are different, this will also hurt the effectiveness of the electronic "Bat Ears".
This thesis addressed the aforementioned two issues in an attempt to enhance the performance of the electronic "Bat Ears". To eliminate the crosstalk in the output of electronic "Bat Ears", we analyzed the output of the electronic "Bat Ears", examined the properties of the crosstalk signal, and eliminated the crosstalk through both computer simulation and newly developed experimental circuits. The crosstalk was identified as the signal received from each ear when there was no obstacle in the front of the electronic "Bat Ears". An analog to digital (A/D) convertor with sampling frequency of around 40 kHz read the signal to a computer or digital signal processor (DSP). The signal saved in the computer or DSP was replayed every time after an emission of ultrasound pulse was made. This signal was subtracted from the received signal in each ear in a synchronized manner to minimize the crosstalk. The crosstalk was significantly decreased using the newly implanted circuits in the "Bat Ears". To compensate the difference in the attenuation properties of ultrasound and audible sound, we proposed an explicit method to construct a matching relationship between the output of electronic "Bat Ears" and the theoretical audible sound. Using the results from our first study, we obtained a great improvement in the current electronic "Bat Ears". The results from our second study would likely be further investigated and implemented in a future version.
Rights: All rights reserved
Access: open access

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